The US Food and Drug Administration has warned that some skin medicated patches such as those used for stopping smoking and other pain relieving patches should not be worn while undergoing magnetic resonance imaging scans or MRIs due to the risk of burns.

Since some of the patches have aluminum, which can be overheated during an MRI scan by the machine's large magnet that can cause the aluminum to overheat and cause skin burns similar to sunburn.

The patches include both brand name and generic products and those purchased over the counter without a prescription.

The FDA issued the Public Health Advisory on transdermal drug patches after learning that a warning was missing on some patches that contain aluminum or other metals in their non-adhesive backing.

The backing is the portion of the patch not in direct contact with the skin. While not attracted to the magnetic field of the MRI, the metal can conduct electricity, generating heat which can cause burns. Users of the patches reported receiving skin burns at their patch site when wearing the patch during an MRI scan.

"The risk of using a metallic patch during an MRI has been well-established, but the FDA recently discovered that not all manufacturers include a safety warning with their patches," said Janet Woodcock, M.D, director of the FDA's Center for Drug Evaluation and Research. "Because the metal in these patches may not be visible and the product labelling may not disclose the presence of metal, patients should tell both their healthcare professional and their MRI facility that they wear a medicated adhesive patch."

The US FDA was alerted to the missing MRI warning on Teva Pharmaceutical's fentanyl transdermal system in January and on investigation, it was found that a similar warning was also missing on a variety of skin, or transdermal, patches delivering medications.

The FDA said that it is reviewing the labeling and composition of all medicated patches to ensure that those made with materials containing metal provide a warning to patients undergoing an MRI and will alert the public as and when this information has been added.

Until then, the agency recommends that people wearing medicated skin patches, including nicotine patches, should talk to a health care professional about their patch at the time they are asked to do an MRI scan.

The doctors will advise the patient about when to remove the patch before the procedure and about replacing it after the procedure and patients should also tell their MRI facility that they are using a patch when they call to schedule their appointment and should repeat this information when filling out their health history questionnaire after arriving for their appointment, said the FDA.